In-Vessel Composting

In-Vessel Composting (IVC) plants treat mixed food and green wastes, operating in enclosed systems that provide temperature and process control and compliance with animal by-products for certain food and animal wastes.

Air is introduced into the vessel to ensure optimisation of natural biological processes in aerobic conditions (aerobic digestion) to ultimately produce a compost output/soil improver for use on land and in landscaping.

Overview

In-Vessel Composting facilities treat green and garden waste with selected food wastes to produce soil improvers that can be used in agriculture, horticulture and landscaping. The treatment process takes between 14 to 20 weeks from receipt to production of the compost/soil improver.

In WikiWaste, In-Vessel Composting is treated as a distinct infrastructure type within the wider Composting category. This page provides a structured view across the national fleet and in the future will connect through to individual facility pages and Local Authority disposal routes

Parameters	Stats.	Units/Year
Number of Operational Facilities	60	number (2024)
Tonnes Received	5,000	'000 tonnes (2024)
abc	00	xyz (2024)
abc	00	xyz (2024)
abc	00	xyz (2024)

The Process

Overall Process

The overall process of In-Vessel Composting is broadly the same as Windrow Composting, but in an enclosed environment and at higher temperatures which leads to the development of slightly different natural aerobic digestion conditions.

Waste facilities must meet certain operational standards (for recovery operations up to 35,000 tonnes per year [2] and for installations up to 75,000 tonnes per year[3] although in many cases the size of the operation is between 20 to 40,000 tonnes per annum).

In order for the compost/soil improver to meet End of Waste Criteria ( in the majority of the UK, this is demonstrated by meeting the Quality Protocol for compost and the associated Quality Standard PAS100.

Compost products and soil improvers are being increasingly used to reduce the demand on peat based composts(peatlands provide efficient carbon storage and unique habitats that many are striving to protect[4]) although some barriers are still being overcome to wider adoption[5]

Differences between IVC and OAW

There are two key differences between IVC and Open Air Windrow Composting:

IVC can reach higher temperatures that can be more accurately controlled than in Open Air Windrow Composting- which results in the destruction of potentially harmful bacteria found in meat or other Food Waste which may have come in contact with meat
IVC occurs in a sealed unit rather than in the open. This means that materials can reach and consistently maintain high temperatures for the required minimum period of time and keeps the material away from outside influences such as weather and wildlife and complies with the management requirements of Animal By-product Material

Sites for both IVC and OAW are often located in agricultural and less rural locations, with a general requirement to locate at least 250 meters from householders to reduce the risk of airborne dust and spores impacting people.

The 4 key stages of the process are set out below.

Stage 1: Initial Processing and First Barrier

The Food Waste which has either been collected separately or with Green Waste is delivered to an enclosed reception area. Any contamination such as plastic bags, bits of metal etc are removed and the remaining material is shredded to a uniform size and consistency (Green Waste may be added to ensure the mixture has a structure to allow air to pass through the material during the treatment process).

From there it is loaded into a first ‘barrier’ which will be a bay/tunnel etc depending on the system used. All the material delivered to a facility, plus the first barrier stage, is considered a ‘dirty area’ under ABPR. The regulations ensure that strict procedures are in place to prevent cross-contamination of ‘clean areas’ (where product is processed and stored) from ‘dirty areas’.

Stage 2: Secondary Processing and Second Barrier

Stage two normally lasts between seven days and three weeks. The material is transferred to the second ‘barrier’, where the composting process continues. Processing in two stages ensures that all parts of the composting mass reaches the required temperature. The oxygen level, moisture and temperature are carefully monitored and controlled during both composting stages to ensure the material is fully sanitised.

Stage 3: Open Air Windrow Processing

Once the sanitisation process is complete the compost is left to mature in an open Windrow Composting area, or an enclosed area, for approximately 10-14 weeks to ensure stabilisation, often termed 'maturation'.

Stage 4: Screening and Final Product Production

Stabilised material is screened, and any remaining contaminants removed, to produce a range of product grades for various end uses such as soil conditioning/a soil improvement material providing it meets the Quality Standard PAS100 which dictates the process standard to ensure that it meets End of Waste Criteria. Any large materials that have not fully broken down in the process (such as larger branches) are taken from the screening process and re-introduced back into the process as outlined above. If large pieces build up over time they are often sent to a Biomass EFW facility.

The different grades of compost can be used for different purposes. Some grades are used as agricultural soil conditioners, others as mulches and others are suitable for landscape gardening or finer grades can be used on golf courses. In some cases the material is blended with other material (for example sand) to produce other products for horticultural use.

Technological Approaches

In-vessel Composting can occur in a variety of technology approaches, which typically process 20,000 to 40,000 tonnes per year for the larger systems, including (left to right). The following are images of the 6 main times of technoclogy approach to IVC.